The incidence of venous thromboembolism over three months was 0.9% with ultrasonography at the groin and back of the knee compared with 1.2% with a full groin-to-ankle scan, reported Enrico Bernardi, M.D., Ph.D., of the Civic Hospital, and colleagues in the Oct. 8 issue of the Journal of the American Medical Association.

The improved detection for whole-leg ultrasonography was confined to the diagnosis of isolated calf thrombosis.

The findings validate clinical practice, which typically includes the two-point examination with compression ultrasonography for symptomatic outpatients, Dr. Bernardi's group added.

The two-point method is easy to learn and can be done on virtually any ultrasound scanner, although it does need to be repeated to confirm that any isolated calf deep vein thrombosis missed on the first exam hasn't spread, the researchers said.

In an accompanying editorial, C. Seth Landefeld, M.D., of the University of California San Francisco and Stanford University in Stanford, Calif., agreed.

Whole-leg ultrasonography would hold an advantage only if a course of anticoagulant therapy for isolated calf thrombosis was preferable to repeating two-point ultrasonography seven to 10 days later, he said.

The whole-leg method can definitively exclude isolated DVT in the calf in a single visit without additional testing.

In the study, the whole-leg method detected deep vein thrombosis more often than the two-point method (26% versus 22%, difference 4.3%, 95% CI 0.5% to 8.1%), which was entirely accounted for by isolated DVT in the calf.

But, treating clots restricted to the calf may not be necessary despite American College of Chest Physicians guidelines to the contrary, Dr. Landefeld said.

The lack of reduction in venous thromboembolism seen in the study and poor evidence for benefit from other studies suggests that "symptomatic but undiagnosed and untreated isolated calf deep vein thrombosis often has a benign course," he said.

The improved detection of isolated calf clots served as a rationale for whole-leg ultrasound, Dr. Bernardi's group said.

Because of this, many patients with suspected DVT have been put on anticoagulants unnecessarily until a skilled ultrasonographer could do the procedure hours or days later, they noted.

A more reasonable approach is to choose two readily available tests initially, coupled with two-point ultrasonography, Dr. Landefeld said.

Options are a clinical prediction rule to determine whether a patient is at risk and a D-dimer test to detect active clot formation.

Anticoagulation can be withheld safely if both are negative or, if not, patients can go on to two-point ultrasonography with a second ultrasound one week later, he said.

In Dr. Bernardi's study, three-month outcomes after whole-leg ultrasound were compared with those after compression ultrasonography of the common femoral and popliteal veins plus D-dimer testing for patients with normal ultrasonography and repeat ultrasonography one week later for those with a positive D-dimer test.

The randomized study included 2,098 consecutive symptomatic outpatients who presented at 14 centers with a first episode of suspected deep vein thrombosis of the lower extremities.

All patients had been spared anticoagulation on the basis of normal initial findings and were then followed for venous thromboembolism.

Other findings included a similar initial prevalence of proximal deep vein thrombosis with the two-point strategy as with whole-leg ultrasonography of the deep vein system (22.1% versus 20.2%).

This confirmed that, in symptomatic outpatients, "the superficial and deep femoral veins are usually not worth investigating," the researchers said.

Whole-leg ultrasound may still be "desirable for patients with severe calf complaints, for travelers, and for those living far from the diagnostic service," they concluded, "but [it] is cumbersome, possibly more expensive, and may expose patients to the risk of (unnecessary) anticoagulation."

Dr. Landefeld reported support by a fellowship at Stanford University and by grants from the S. D. Bechtel Jr. Foundation, the National Institute on Aging, and the John A. Hartford Foundation. He reported no conflicts of interest.